FEV Generic Architecture

To achieve the aims of reducing energy consumption and CO2 emissions, Fully Electric Vehicles (FEVs) need to reach a significant market share. However, the advent of FEVs in mass production presents new challenges to automotive manufacturers due to the relative immaturity of the new building blocks, which may impact on the FEV’s safety and reliability. Among the most important of these is the electric powertrain. Therefore, the main aim of the HEMIS project is to design a PHMS for the powertrain in order to enhance the safety and maintainability of FEVs.

In order to do so, a generic FEV architecture has been defined describing common features of the FEVs, as the HEMIS project is not focused on any specific vehicle. This architecture focuses on the electrical powertrain and those systems that have an impact on the operation of the electrical powertrain.

The electrical powertrain corresponds to the Electrical Transmission system of Figure 1 which comprises the Electrical Machine and the Control. As the Electrical Transmission components are assumed to be monitored by the PHMS, sensor outputs are indicated from the Control and Electrical Machine.

Figure 1: HEMIS generic FEV architecture

The generic FEV architecture forms the basis of the RAMS analysis of the vehicle, whose main goal is to improve the safety of the FEV, in order to identify corrective actions to mitigate the hazard. This is a key aspect to define the PHMS.

Firstly, the preliminary hazard analysis (PHA) has been carried out by reviewing the mission of a system together with the environment around the system and its uses. The outcome of the PHA is to translate system hazards into design constraints, or functional safety requirements. Afterwards each hazard was assessed in terms of their potential consequences, likelihood of occurrence and opportunities for the driver to influence the outcome according to ISO 26262. A risk graph is then used in order to establish and classify the associated risks in terms of the Automotive Integrity Levels (ASILs).

ID

Hazard

Severity

Exposure

Controllability

ASIL

FHAZ_01

Undemanded vehicle  acceleration

S3

E4

C3

D

FHAZ_02

Undemanded vehicle deceleration

S3

E4

C3

D

FHAZ_03

No vehicle acceleration

S3

E4

C3

D

FHAZ_04

No vehicle deceleration

S3

E4

C3

D

Table1 Hazard analysis and risk classification results

For evaluating the safety of the FEV, potential functional failure mechanisms of a generic electrical powertrain were analysed, based on the hazard analyses, using the Failure Modes and Effects Analysis (FMEA), Table 2, and Fault Tree Analysis (FTA), Figure 2. FMEA and FTA are complementary methods: a FTA is a logic diagram that displays the interrelationships between a potential critical event (accident) in a system, a FEV, and the reasons for this event.; and the FMEA is a bottom-up, inductive analytical method which studies the effects of single component or function failures on the system or subsystem.

Figure 2 Fault tree for hazard “No vehicle acceleration” 

System and Functions

Failure Mode

Subsystem Effect

System Effect

RPN

Electrical Transmission

 

 

 

 

Torque supply function

Failure to operate when required

No torque

No acceleration

6

Torque supply function

Output higher than required

Excessive torque

Excessive acceleration

12

Table 2 Example of results from FMEA at FEV level

The FMEA approach provided a mechanism for identifying and prioritizing those failure modes that are considered to require corrective action in order to ensure that functional safety targets are satisfied. In order to select the key physical FEV powertrain characteristics which the HEMIS PHMS will monitor, a FMEA has been developed at subsystems level, Table 3, based on the refined powertrain architecture description, Figure 3.

Figure3 HEMIS generic electrical powertrain architecture

System and Functions

Failure Mode

Subsystem Effect

System Effect

RPN

Inverter

 

 

 

 

Switch the IGBTs to chop the DC current

Short circuit

Gate driver cuts the current flow

Rotor may block

4

Stator Windings (Induction Machine)

 

 

 

 

Provide required current path

Open circuit

Decreased current flow

Unreliable Stator Magnetic field

6

Table 3 Example of results from subsystems FMEA for Electrical Transmission

The objective of the HEMIS project is to design a PHMS which provides information on the failsafe state of the electric powertrain and enables to apply a condition based maintenance policy on its subsystems, this project focuses on the recommended actions or mitigation techniques which reduce or eliminate the risk of failures modes of Electrical Transmission. The selected risk acceptance principle is the Minimum Endogenous Mortality (EN 50126) which is based on an individual risk verifying that it is reached adding a PHMS reducing the risks associated with failures of the electrical powertrain.

Based on the failure modes analysis of the electrical powertrain, those electrical powertrain failure modes that are considered to require corrective action in order to ensure that functional safety targets have been identified (Table 4).

Table 4 Example of failure modes assessment to select the ones be monitored

 

 

 

 

 >return to Results Overview

 

 

 

 

 

 

 

Project acronym:
HEMIS

Project name:
 Electrical powertrain Health Monitoring for Increased Safety of FEVs


Project reference:
FP7-ICT-314609

Start date: 01/06/2012
End date: 28/02/2015


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